The present invention is related generally to compression and condensation of turbine exhaust steam, and particularly to reducing the temperature difference between the inlet of a cooling medium (e.g., sea water or fresh water) in a counter current heat exchanger and the temperature of the turbine exhaust steam. The invention is a new xe2x80x9ccondenser systemxe2x80x9d which will replace conventional condensers normally utilized in power plants.
A steam turbine is a well-known device for converting a heated gas (in this case steam) into either mechanical or electrical energy, depending upon the driven device. In the heat/power cycle of the turbine, steam enters the turbine at elevated pressure and temperature, and the inherent heat energy of the steam is converted into rotational energy.
The generally accepted heat/power cycle for central power station units requires the turbine discharge exhaust pressure to be as low as possiblexe2x80x94i.e. high vacuum. The high vacuum is intended to maximize the removal of available energy per unit mass of steam, thereby maximizing the thermodynamic efficiency from the steam turbine.
A condenser, generally a shell and tube heat exchanger, is located at the steam exit of the turbine to condense the turbine discharge steam flow for its reuse as a condensate in the heat power cycle. The cooling medium, either sea or fresh water, passes through the tubes while the exiting steam condenses within the condenser shell on the exterior surface of the tubes, ultimately falling to the bottom of the condenser for reuse in the heat power cycle.
In the current power plant state-of-the-art, large power station units are equipped with two identical low pressure double flow turbines which operate in parallel. In effect, the low pressure steam flow is divided into four parallel flows exiting four last-stage turbines, at approximately 300 m/sec.
Prior art low pressure turbine exhaust shell designs are generally inefficient, since the existing designs produce an excessive pressure drop in the exhaust steam flow, caused by obstructions in the steam path in combination with a lack of proper steam ducting to the condenser which creates undesirable swirling and a decrease in system efficiency.
The present invention provides a system for compression and condensation of turbine exhaust steam in combination with a counter current heat exchanger using sea water or fresh water or air as the cooling medium, which increases the power output of the steam turbine.
The system causes an increase in vacuum at the turbine exhaust, which in turn produces an incremental increase in the rotational energy extracted from the low pressure section of the turbines, due to a reduction in the temperature difference between the inlet of the cooling medium and the temperature of the exhaust steam, making the system very efficient.
There is thus provided in accordance with a preferred embodiment of the present invention a steam turbine exhaust system comprising a dual section vessel including a first section being a turbine exhaust steam enclosure and a second section being a condensate water vessel, both sections being connected by a system of water columns.
The system of water columns comprising moderate diffusers for retaining turbine steam velocity without increase in pressure, towards impact with the water columns, and an integral condensate recirculation connection having one end immersed in the condensate water vessel for collecting warm condensate water and transporting to a counter current heat exchanger.
Further, in accordance with a preferred embodiment of the present invention a counter current heat exchanger is provided through which the recirculated condensate water is cooled and recirculated.
The heat exchanger controlling the temperature of the condensate, so that the condensate exit temperature being within a small temperature difference to a cooling medium through the heat exchanger, then returning the condensate at the reduced temperature for distributing through water dispersion pipes connected to the ends of the diffusers.
At the colliding location, between exhaust steam and condensate water, the exhaust steam continues to flow as xe2x80x9ctwo phase flow,xe2x80x9d where the steam being compressed and simultaneously condensed produces an incrementally lower exhaust steam temperature and higher vacuum at the exhaust of the last stage turbine. This vacuum being incrementally higher than the condensate water vessel vacuum due to a rise in condensate temperature during its downward flow in the water columns.
Still, further in accordance with a preferred embodiment of the present invention, ends of the diffusers are immersed sufficiently in the condensate water so that a majority of a height of the water columns is in the ends of the diffusers, and the ends of the diffusers are arranged for receiving, compressing and condensing the exhaust steam from the last turbine stage, colliding with a cold condensate.
Preferably temperatures are generally uniform on top portion of the water columns.
Still further, in accordance with a preferred embodiment of the present invention the diffusers are sufficiently moderate so as to maintain an almost constant steam velocity until the exhaust steam is close to impact with the water columns. After the turbine neck, the diffusers are preferably enveloped up to the condensate water vessel.
A steam turbine exhaust system, wherein at least one of the said water columns downstream of one of said diffusers having integral connection for recirculating cold condensate, said water columns being inmmersed in the lower portion of said condensate water vessel.
Still further, in accordance with a preferred embodiment of the present invention, a second such steam turbine exhaust system is provided, wherein turbine exhaust steam exits from the first steam turbine exhaust system, collides with recirculated condensate water, flows to the second steam turbine exhaust system and collides with water columns of the second steam turbine exhaust system which results in double compression with a corresponding increase in condensate temperature.